1. Technical Field of the Invention
The present invention relates to a drive unit in which an electric motor is used as a power source, and more particularly, to a cooling system in a drive unit for an electric vehicle or a hybrid drive unit.
2. Related Art
When an electric motor is used as a drive source for a vehicle, the load exerted on the electric motor varies significantly according to the running conditions. Accordingly, in order to manage the heat generated under a heavy load, cooling is necessary. Also, an electric motor requires a controller, e.g., an inverter in the case of an alternating current electric motor. Since a controller such as an inverter is connected to the electric motor with a power cable, it can be separated from the electric motor and mounted in an appropriate position. However, for mounting convenience in a vehicle, arrangements have also been used in which the inverter is integrated with the electric motor.
However, when the controller is integrated with the electric motor, not only does the temperature of the controller rise due to the heat generated by its own elements, but it is also affected by the heat from the electric motor and therefore requires cooling. Therefore, conventionally, where an electric motor has an integrated inverter, a heat sink for mounting the inverter is attached to a drive unit case, and a cooling water channel is formed between the heat sink and the drive unit case so as to simultaneously cool the motor and the inverter (see Japanese Patent Application Laid-Open No. 7-288949).
However, according to the conventional art construction as described above, because the same cooling water simultaneously cools the inverter and the electric motor, there is a problem of the heat from the electric motor being transferred to the inverter by the cooling water and the case.